Less Holes in Roof

A ranch home....I have a situation where I would like to vent 2 bathrooms that are 25' apart and the kithcen stove. Do I need 3 seperate holes in the roof or can I combine the vents in the attic and exit the roof with only one or two holes?

I don't think you want to combine the stove and bathroom vents. Fantec makes a multi location fan system, so you can combine the two bathrooms. See what they say about a kitchen. There may be other systems available.

Problem with the stove is grease accumulation. The filters aren't perfect and you want that to be as short as possible. See what other thoughts you get...

Do I need 3 seperate holes in the roof or can I combine the vents ...?

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My bathroom fans have backflow prevention flappers in them, and I can imagine I could run them into one outlet if both lines were horizontal and I did not have to be concerned about condensation running back into either. But if you must go vertical, something like a remote fan such as Jim has mentioned would likely be far better ... and I would definitely keep the kitchen vent on a (fire code?) line of its own.

The dampers on a typical fan is a very poor air stop...they aren't really designed to be joined into one outlet. You could probably engineer something that would prevent blowing that lovely smell from a big dump from one room to the other, but it's probably better to rely on something already designed for it. The ductwork would need wye's and probably to become larger after they were joined. That would create a larger hole since you'd need a larger vent.

One thing that I really like in my house is a combo circular skylight, vent, ceiling light. That makes more holes, since the exhaust is not done on the same hole as the skylight flashing (it's entirely separate). But, that 10" hole in the ceiling is the equivalent of a 300W lightbulb, and doesn't cost electricity. A skylight produces much more light than a typical window, and it does it during more of the day. www.solatube.com

When I first read your post, I missed the kitchen stove reference; I thought you meant plumbing vents!

The only way I can think of to vent 2 bathrooms through one pipe, would be to use an in-line fan on the pipe they share, and have it be controlled from either bath. So when you turn on the fan, air is drawn from both.